Functional Analysis of a Complement Polymorphism (rs17611) Associated with Rheumatoid Arthritis

Abstract

Complement is implicated in the pathogenesis of rheumatoid arthritis (RA); elevated levels of complement activation products have been measured in plasma, synovial fluid, and synovial tissues of patients. Complement polymorphisms are associated with RA in genome-wide association studies. Coding-region polymorphisms may directly impact protein activity; indeed, we have shown that complement polymorphisms affecting a single amino acid change cause subtle changes in individual component function that in combination have dramatic effects on complement activity and disease risk. In this study, we explore the functional consequences of a single nucleotide polymorphism (SNP) (rs17611) encoding a V802I polymorphism in C5 and propose a mechanism for its link to RA pathology. Plasma levels of C5, C5a, and terminal complement complex were measured in healthy and RA donors and correlated to rs17611 polymorphic status. Impact of the SNP on C5 functionality was assessed. Plasma C5a levels were significantly increased and C5 levels significantly lower with higher copy number of the RA risk allele for rs17611, suggesting increased turnover of C5 V802. Functional assays using purified C5 variants revealed no significant differences in lytic activity, suggesting that increased C5 V802 turnover was not mediated by complement convertase enzymes. C5 is also cleaved in vivo by proteases; the C5 V802 variant was more sensitive to cleavage with elastase and the “C5a” generated was biologically active. We hypothesize that this SNP in C5 alters the rate at which elastase generates active C5a in rheumatoid joints, hence recruiting neutrophils to the site thus maintaining a state of inflammation in arthritic joints.

Development and characterization of novel anti‐C5 monoclonal antibodies capable of inhibiting complement in multiple species

“…The mAb were also tested for their capacity to block the atypical cleavage of C5 by NE, a process that has been implicated in the generation of C5a and MAC at inflammatory sites such as in the rheumatoid joint and cystic fibrosis lung; mAb that inhibited this cleavage might therefore have additional value as therapeutics. The mAb 4G2 strongly inhibited NE‐mediated C5 cleavage and C5a generation in vitro , whereas the other two novel mAb weakly inhibited atypical C5 cleavage (Fig.…”

Complement C5 Contributes to Brain Injury After Subarachnoid Hemorrhage

“…This SNP has also been linked to poor outcome after pneumococcal meningitis [31], adverse cardiovascular outcomes [37], and periodontitis [38]. Recently, the functional basis for these disease associations was clarified [39]. Allele G of the C5 rs17611 SNP causes a missense mutation in the C5 gene, increases the rate of proteolytic activation of C5 and C5a generation.…”

Complement Polymorphisms in Kidney Transplantation: Critical in Graft Rejection?

“…The C5 gene is highly polymorphic . One of the identified SNPs, rs17611, a missense polymorphism, is associated with an increased C5 turnover resulting in a significant decrease of plasma C5 and increase in C5a levels . This could in turn enhance chemoattraction and potentially also membrane attack complex formation resulting in more severe graft injury.…”

“…Complement regulators, both fluid‐phase and membrane‐bound, control amplification of the complement cascade and protect (self‐)cells against the deleterious effects of complement activation . Numerous polymorphisms in complement proteins have been identified thus far, including several polymorphisms that result in distinct functional differences (Figure ) . For instance, serum mannose‐binding lectin (MBL) levels are largely influenced by polymorphisms both in the promotor and the coding part of the MBL2 gene .…”